1. Field of the Invention
The present invention relates to a Group III-V complex vertical cavity surface emitting laser (hereinafter refer to VCSEL) diode manufactured using GaN-system III-V nitride and a manufacturing method thereof.
2. Description of the Related Art
In general, a VCSEL manufactured of GaN-system III-V nitride can emit near ultraviolet light of 400 nm wavelength and blue light, so it can be used in a high-capacity information storage apparatus. Also, the surface emitting laser oscillates in a single longitudinal mode as opposed to an edge emitting laser.
Such a surface emitting laser diode, as shown in FIG. 1, usually includes a cavity 10 and Distributed Bragg Reflectors DBR 20 and 30 of reflectance of 99.9% or greater, respectively provided on the lower and upper surfaces of the cavity 10. The cavity 10 has an active layer 11 formed of InGaN multi quantum wells, and n-AlGaN and p-AlGaN carrier restrictive layers 12 and 13 respectively formed on the lower and upper surfaces of the active layer 11. The DBRs are generally one of two types. One type uses semiconductor materials which have similar lattice constants and are capable of epitaxial growth, such as GaAs and AlAs, and the other type uses a dielectric material such as SiO.sub.2, Al.sub.2 O.sub.3, TiO.sub.2, or ZnO.sub.2. In the former case, current can be injected via semiconductor, and the quality of the thin film is excellent. Here, a usable DBR has a greater bandgap energy than that of a light of wavelength self-stimulating in the active layer 11, and the self-stimulating light must not be absorbed in the DBR. It is preferable that the difference in the refractive index between two layered OBR materials is great. In the GaN-system VSCEL diode as shown in FIG. 1, the DBRs 20 and 30 can be formed of a semiconductor material such as alternating layers of GaN 22 and 32 and AlN or AlGaN 21 and 31. Among them, AlGaN and AlN 21 and 31, containing at least 30% Al, have significantly high bandgap energy. Accordingly, when current is injected via the DBRs composed of the AlGaN and AIN 21 and 31, a voltage for driving them significantly increases, so that problems due to generation of heat may be created. Furthermore, when the DBR is comprised of the GaN 22 and 32 and AlN 21 and 31 having the greatest difference in refractive index, at least 20 pairs of layers must be stacked to obtain a desired high reflectance. Furthermore, a very narrow wavelength width in a high reflectance region makes it difficult to design a VSCEL diode. A slight deviation from the thickness of the cavity 10 or a small change in the composition of the active layer 11 can ruin self-stimulating conditions.
FIGS. 2A and 3A show reflectance of DBRs formed by stacking GaN and AlN with a thickness of .lambda./4n (.lambda. is a wavelength, and n is refractive index) to 15 pairs and to 30 pairs, respectively. Here, the refractive indices of GaN and layers are set to 2.67 and 2.15, respectively, and a central wavelength is set to 430 nm. From FIG. 2B being an extended graph of FIG. 2A, we can see that sufficient reflectance cannot be obtained by the 15-pair DBR and that the width of a spectrum indicating high reflectance is very narrow. From FIG. 3B being an extended graph of FIG. 3A, we can recognize that sufficient reflectance can be obtained by the 30-pair DBR but that the width of the spectrum indicating high reflectance is still too narrow. However, a more serious technical problem is that manufacture of the DBR with so many pairs is difficult due to slow and difficult crystal growth of GaN/AlN in contrast with the DBR manufactured of GaAs/AlAs.
A dielectric DBR can be utilized in order to overcome such defects, but it can be applied to only an upper DBR. A lower DBR must be manufactured by the crystal growth method in order to grow the cavity.